1. Field of the Invention
The present invention relates to a magnetic tape on which at least a servo pattern is formed.
2. Description of Related Art
A magnetic tape finds various applications such as an audio tape, a video tape, and a computer tape. Particularly, in the field of a data backup tape used for data backup in a computer, tapes having a storage capacity of hundreds of Gbytes per volume have been commercialized along with the increase in capacity of a hard disk targeted for backup. In the future, the increase in capacity of a backup tape is indispensable so as to address the further increase in capacity of a hard disk.
Along with the increase in capacity of a magnetic tape, it is necessary to perform high-density recording with respect to a magnetic tape. Examples of the high-density recording include a technique of recording data onto a magnetic tape while shortening a recording wavelength of data (wavelength shortening technique) and a technique of recording data onto a magnetic tape while narrowing a track width in which the data is to be recorded (track narrowing technique).
Furthermore, in order to allow a magnetic head to trace an intended track exactly, a servo signal is recorded previously on a magnetic tape. For example, as shown in FIG. 5A, in a magnetic tape under the Linear Tape Open (LTO) specification, a plurality of data zones 103 are formed in a longitudinal direction of a magnetic tape 101, and servo bands 102 are formed between the respective data zones 103. A data signal can be recorded in the data zones 103, and a servo signal is recorded previously in the servo bands 102 by a servo writer or the like. FIG. 5B is an enlarged view of a Z-portion shown in FIG. 5A. As shown in FIG. 5B, each servo band 102 include a plurality of servo patterns in a substantially truncated chevron shape. According to the LTO specification, one servo frame includes a first servo pattern group 102a composed of 5 servo patterns tilted in a first direction with respect to the longitudinal direction of the magnetic tape 101, a second servo pattern group 102b composed of 5 servo patterns tilted in a second direction opposed to the first direction, a third servo pattern group 102c composed of 4 servo patterns tilted in the first direction, and a fourth servo pattern group 102d composed of 4 servo patterns tilted in the second direction. One servo frame has a length of 200 μm.
When information is reproduced from the magnetic tape 101 by a recording and reproducing apparatus, a data signal recorded in the data zones 103 is read by a data head, and a servo signal recorded in the servo bands 102 is read by a servo head, whereby the data signal can be read while a magnetic head is positioned exactly on an intended track on the magnetic tape 101. When tracking servo is performed, a servo signal in one servo frame is read, and thereafter, the amount of a positioning control of the magnetic head is updated. More specifically, the position of the magnetic head is corrected every time the magnetic tape 101 is allowed to travel by 200 μm.
For example, Patent Document (JP 2005-056500 A) discloses a configuration in which a servo signal is recorded or reproduced magnetically with respect to a magnetic tape.
However, in the configuration shown in FIGS. 5A and 5B, one servo frame has a length of 200 μm, so that there is the following problem: the number of samples of a servo signal per unit time is small, and the traceability of the magnetic head with respect to the magnetic tape is low. In particular, when the magnetic tape is deformed in a width direction due to the influence of temperature and humidity, the traceability of the magnetic head with respect to the magnetic tape decreases largely.